1. Field of the Invention
The present invention relates to an illumination device, a projection video display device loaded with the illumination device, and a fly-eye lens to be incorporated in the illumination device, and is more particularly directed to an arrangement, in which a laser light source is used as an emission light source.
2. Disclosure of Related Art
Conventionally, in a projection video display device (hereinafter, called as a “projector”), there has been used a lamp light source such as an ultra-high pressure mercury lamp, a metal halide lamp, or a xenon lamp, as an emission light source. Also, in recent years, a projector incorporated with a solid-state light source such as a semiconductor laser, as an emission light source, has been developed. The laser light source has been noticed as an emission light source for a next-generation projector, in view of a point that the laser light source has a superior performance of rendering a wide color space with high luminance and high precision.
In the case where a laser light source operable to emit a light flux having a large solid angle is used as an emission light source, it is necessary to properly convert laser light to be emitted from the laser light source into parallel light. In performing the conversion operation, it is possible to use a lens, a diffraction grating, or a like device, as means for converting laser light into parallel light. In converting laser light into parallel light by using a lens, a diffraction grating, or a like device, an intensity distribution of laser light to be obtained after transmission through the lens, the diffraction grating, or the like device may become non-uniform.
For instance, as shown in FIG. 12A, in the case where a light flux to be emitted from a laser light source is converged in Y-axis direction by a cylindrical lens, an intensity distribution of laser light to be obtained after transmission through the cylindrical lens is as shown in FIG. 12B. FIG. 12B is a diagram schematically showing an intensity distribution of laser light to be obtained after conversion into parallel light by using the optical system shown in FIG. 12A in monochromatic expression, using an optical simulation software. As shown in FIG. 12B, the light intensity is increased, as the color is closer to white. In this arrangement, the light intensity distribution is non-uniform in Y-axis direction.
In some cases in an optical system for a projector, a fly-eye lens is provided as means for guiding uniform light to an imager (such as a liquid crystal panel). In such a case, the fly-eye lens is provided at a position posterior to an optical component such as the cylindrical lens or the diffraction grating. However, as described above, the intensity distribution of laser light to be obtained after transmission through a cylindrical lens or a like device may become non-uniform. Accordingly, in the case where laser light, after conversion into parallel light by a lens or a like device, is guided to an imager by a fly-eye lens, illuminance non-uniformity may be generated in the imager, which may generate non-uniformity in a projected image.